This invention relates to flame retardation, and more particularly to the use of a specific class of compounds as flame retardants for polymers.
Improvement of the fire resistant properties of polymers has long been a goal of polymer compounders. Fire resistance is typically evaluated by the UL-94 test of Underwriters Laboratories (ASTM procedure D3801). In this test, the desirable V-0 rating is given to polymers of which specimens do not burn with flaming combustion for more than 10 seconds after application of a test flame, and specimens do not burn with flaming combustion for a time exceeding 50 seconds upon 2 flame applications to each of 5 specimens; i.e., the total "flame-out time" (FOT) for said samples is not greater than 50 seconds.
Various types of chemical compounds may be employed as flame retardancy additives. They include halogenated and especially brominated compounds and phosphate-based compounds. Such additives are often employed in combination with anti-drip agents such as fluorocarbon polymers, and synergists such as antimony halides.
It is desirable in some instances to employ exclusively phosphate-based compounds. Among the compounds known to be useful for this purpose are the bis(diaryl phosphate) esters of dihydroxyaromatic compounds, as illustrated by resorcinol bis(diphenyl phosphate), hydroquinone bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate). These compounds, however, frequently also have undesirable effects on the high temperature properties of the polymer substrates, as demonstrated by a pronounced decrease in heat deflection temperature (HDT) and/or glass transition temperature (Tg).
It is of interest, therefore, to develop resinous blends containing phosphate-based flame retardant additives having a minimum effect on the high temperature properties of the blends.